In order to improve the performance and lower the cost/performance ratio of superconducting coated conductors, an important goal is to increase the critical current density (Jc) in magnetic fields (H). In bulk melt processed materials, microstructural modification in ternary REBa2Cu3O7−x films (hereafter referred to as RE-123 where RE is a rare earth metal) has been shown to increase the irreversibility field. In films, there is already much pinning associated with the growth process and hence improved performance through microstructural modification is nontrivial.
There have been numerous studies of RE-123 films. Advantages of the RE's over yttrium (Y) include lower processing temperatures and wider processing windows (for the RE's smaller than Y), and the possibility for introducing point defects arising from cation exchange between the RE and barium (Ba). However, so far, there has been no clear demonstration of enhanced pinning in RE-123 films compared to high-quality YBa2Cu3O7−x (YBCO). It is noted, however, that one very recent report of a ternary RE-123 composition has indicated an improved irreversibility field in about 100 nm thick films on single crystals compared to single component RE-123's. The determination of whether there are any real improvements in pinning when comparing different RE-123 samples is obscured by the different critical temperatures (Tc's), unknown amounts of cation exchange, and different levels of crystallinity associated with the different optimum growth temperatures.
It is an object of the present invention to provide mixed rare earth barium cuprate compositions where there is a low ion size variance of the rare earth ions.
It is another object of the present invention to provide mixed rare earth barium cuprate compositions with a low ion size variance of the rare earth ions, the compositions yielding higher Jc's in comparison to a conventional YBCO under similar conditions.